1. Field
The present invention relates generally to telecommunications, and, more specifically, to methods, apparatus, and articles of manufacture for multiplexing multiple users and supporting feedback in cellular radio networks.
2. Background
A modern communication system is expected to provide reliable data transmission for a variety of applications, including voice and data applications. Multi-user communications may include a transmitter sending data to multiple receivers, and several transmitters sending data to a receiver. Cellular communication systems employ multi-user communications, for example, between a base transceiver station (BTS) and multiple mobile stations (MSs) within the sector served by the BTS. Known multi-user communication systems are based on frequency division multiple access (FDMA), time division multiple access (TDMA), code division multiple access (CDMA), and perhaps other multiple access communication schemes.
A CDMA system may be designed to support one or more CDMA standards, such as (1) the “TIA/EIA-95 Mobile Station-Base Station Compatibility Standard for Dual-Mode Wideband Spread Spectrum Cellular System,” (2) the “TIA/EIA-98-C Recommended Minimum Standard for Dual-Mode Wideband Spread Spectrum Cellular Mobile Station,” (3) the standard sponsored by a consortium named “3rd Generation Partnership Project” (3GPP) and embodied in a set of documents including documents known as 3G TS 25.211, 3G TS 25.212, 3G TS 25.213, and 3G TS 25.214 (the “W-CDMA standard”), (4) the standard sponsored by a consortium named “3rd Generation Partnership Project 2” (3GPP2) and embodied in a set of documents including “C.S0002-A Physical Layer Standard for cdma2000 Spread Spectrum Systems,” the “C.S0005-A Upper Layer (Layer 3) Signaling Standard for cdma2000 Spread Spectrum Systems,” (5) the 1xEV-DO standard “TIA/EIA/IS-856 cdma2000 High Rate Packet Data Air Interface Specification,” as well as other standards.
A TDMA system may implement the standards known as Global System for Mobile Communications (GSM). GSM-based networks are widely deployed throughout the world. General Packet Radio Service (GPRS) and its enhanced version known as Enhanced Data rates for GSM Evolution (EDGE) are data services available at some GSM-compatible mobile stations (e.g., cellular telephones). GSM, GPRS, and EDGE may also be collectively referred to as GSM EDGE Radio Access Network or GERAN.
GERAN air interfaces may use frequency hopping. Frequency hopping is a technique that provides frequency diversity over time. A frequency hopping system transmits on a different carrier frequency during every transmission time unit or slot, which typically has a duration of twenty milliseconds. Consecutive hops from one carrier frequency to another are generally made between non-contiguous carrier frequencies to reduce frequency-selective fading of consecutive frames, i.e., to reduce the probability that blocks in consecutive frames will not be correctly decoded at a receiver.
The demand for wireless services continues to increase, while the radio spectrum is either fixed for given wireless applications or available at high cost. Therefore, increased ability to provide services within a fixed spectral allocation is a desirable attribute of wireless systems, including GSM-based cellular systems.
Internet protocol (IP) is used to transport data packets (datagrams) across many networks, most notably the Internet. Voice may be encapsulated in IP packets and transported as data over such networks. In fact, voice over IP (VoIP), also known as Internet telephony or IP telephony, is a fast-growing application of IP-based networks. A call connecting a mobile station to another telephone terminal may be routed using VoIP along at least some portion of the route between the mobile station and the other terminal. Such a call may be converted between VoIP and another protocol at the air interface of the cellular network serving the mobile station. It may be preferable, however, to have end-to-end IP-based connectivity, assuming this is feasible under existing system constraints.
One problem with transmitting IP datagrams over a GERAN air interface is the latency of feedback information inherent in the GSM standards. Typically, a GERAN system will transmit twelve blocks of twenty millisecond duration each, and then send a polling request to the receiver (e.g., to a mobile station or a BTS), asking the receiver to inform the transmitter about the status of the sent blocks. Thus, an acknowledgement of the first block in a twelve-block series of blocks will be received about 240 milliseconds later, or with even greater latency. End-to-end acknowledgements of a VoIP call might take sill longer because of additional en route delays. This is typically too much latency for live telephone conversations. Furthermore, link quality in a mobile environment may deteriorate rapidly, and a delay of 240 milliseconds may be too long for providing timely link quality indications. Still further, additional aspects of cellular system operation may benefit from decreased latency of feedback mechanisms.
There is therefore a need in the art for methods and apparatus that increase spectral efficiency of wireless systems. There is also a need in the art for shortening feedback latency in GERAN-based and similar wireless systems. Moreover, extensive modifications of deployed equipment may be expensive, and compatibility with existing customer equipment may be desirable from a marketing perspective. Therefore, there is a need in the art to address the above-mentioned deficiencies while preserving compatibility with currently-existing GERAN mobile stations and avoiding extensive changes to cellular network hardware serving such stations.